Whenever the costs of drilling of a borehole are mentioned, they often seem exorbitant. However, the various aspects of the drilling process that make the final cost can be broken down in order for the client to understand just what he or she is paying for.
The drilling journey starts with the mobilization of the drilling rig and all the other equipments and materials to the site. The rig is then set to the best position before commensing of the works.
The actual drilling then begins, where the open hole is drilled into the required diameters and depth. Once the borehole has been drilled, the unstable lengths of the borehole are steel cased in an effort to reinforce the ‘tube’. Plain and screen casings are properly aligned following the design recommended.
The borehole is then gravel packed to avoid any contamination from shallow sub-surface water. Gravel packing is an important step because the aquifer could contain silt. Without gravel, sand would damage the pump and lead to gradual ‘siltation’ of the well.
Next is the borehole development, which is done through air or water jetting. This is an extremely vital element as it repairs the damage done to the aquifer during the course of drilling by removing clay and other additives from the borehole walls. It usually results in longer borehole life, greater pumping efficiency and enhances a more constant yield.
Determining the yield of the borehole
The package is also inclusive of a 24-hour test pumping to determine the borehole yield. In order to most accurately gauge the yield of a borehole an aquifer test is performed. This involves installing a test pump and pumping borehole water using a fixed set of variables; a given time at a given rate, and then assessing the test’s impact on the water level in the borehole.
Maximum yield is achieved by increasing the abstraction rate, ensuring optimum drawdown of water in the borehole.
The test pumping unit
Recovery tests are also done immediately after the 24-hours test pumping and the borehole water collected for chemical analysis.
Finally, the borehole is covered to protect it from the elements and vandalism.
